The present invention relates to a system for keying video information to the electron beam deflection voltage and has particular application in cathodoluminescent display devices for determining the position of the beam.
In many display devices, such as conventional cathode ray tubes and more recently in flat image display devices which utilize a plurality of electron beams, it becomes necessary to key the video information to the position of the electron beam. This keying enables the modulation of the electron beam at the precise instant of time for the activation of a specific phosphor element on the display screen. Heretofore, when the position of the electron beam had to be sensed, a plurality of electrodes were incorporated on the screen. The scanning of the electrodes by the electron beam charged the electrodes which was sensed, thereby indicating the instantaneous position of the electron beam. The use of such sensing electrodes, however, necessitates a modification in the display device, be it a cathode ray tube or a flat image display device, by incorporating the number of electrodes on the screen as well as the number of leads through the envelope of the device.